1. Field of the Invention
The techniques disclosed in this patent application are enhancements to a system for surgically surveying, and interrogating cellular telephone systems and surgically neutralizing components of such systems. The systems in which the enhancements are implemented are described in the U.S. national stages Ser. Nos. 12/065,225 and 12/280,716. Such systems may be termed in the following surgical interferers. The enhancements to the systems of Ser Nos. 12/065,225 and 12/280,716 enable the enhanced system to continue to survey and interrogate cellular telephone systems despite the presence of either co-located or temporally adjacent interferers designed to suppress signals from the cellular telephone system. In the terminology used in the relevant arts, the enhanced surgical interferer can “look through” the signals produced by the interferers.
2. Description of Related Art
Prior art describes systems that employ interference to neutralize components of cellular telephone systems use broad-based nonspecific interfering techniques. An important class of such interferers are reactive interferers, which listen to the signals being produced by the cellular telephone system whose components are to be neutralized and then produce interfering signals based on what they have heard and the kind of neutralization required. In the following, this listening activity may be termed acquiring the environment of the cellular telephone system. The environment may be termed the cellular environment. The interfering signal produced by the reactive interferer of course makes listening to the environment impossible, and because the environment is dynamic, a reactive interferer must cease producing the interfering signal in order to again acquire the environment. A period during which a reactive interferer has ceased broadcasting the interfering signal in order to listen to the environment is termed in the following a hole in the interfering signal. Of course, if a number of reactive interferers are in operation, they must agree as to when the holes will occur and how long the holes will be.
Prior-art reactive interferers generally do not do complex analysis of the environment they acquire during a hole. Typically, they perform spectral analysis which simply determines where there is energy present in the environment and then produce interference signals which interfere with the detected energy. Some systems may take this a step further and attempt to characterize the signaling enough to minimize false alarms. However, the analysis techniques cannot acquire deeper structures from the signaling environment such as whether the signal is a beacon, what the parameters carried in the beacon are, or whether the signal is being generated by a frequency hopping phone that is connected to some potentially threatening device. As set forth in PCT/US2007/063493, techniques are available that permit acquisition of such deeper structures and detection of potentially-threatening cellular telephones and that further permit generation of interfering signals which can neutralize potentially threatening cellular telephones without interfering with cellular telephones that are clearly non-threatening. These techniques, however, require access to access to a wireless device's forward link the beacon and related signals which are provided to the cellular device in the forward link and that govern subsequent interactions between a wireless device and the base station. Acquisition of the cellular environment at this level is not possible in the presence of a signal from a broad-based interferer.
Prior art suggests other schemes which permit a receiver to acquire the cellular environment in the presence of an interferer. One approach is canceling the signal produced by the interferer out of the signal received by the receiver. However this approach has serious practical limitations when used with cellular environments because of propagation and dynamic range issues. For example, one can directly sample or perhaps generate a copy of the interfering waveform, negate it, and combine it directly with the incoming RF signal. However, the waveforms used in the cellular systems have wavelengths on the order of inches. Apart from the stringent sub nanosecond calibration tolerance issues raised by such wavelengths (bringing into question manufacturability in quantity), the effects of multipath (e.g., reflections) on the actual interferer signal will, in either case, cause time phase delays and instead of canceling the waveform may enhance it. Even if the technique is partially successful in canceling some parts of the waveform it is likely that the unsuppressed portions of the signal will cause the automatic gain control features common to most receivers to render the receiver incapable of listening to the signals of interest at uncontrollable times. Another shortcoming is that this approach will not necessarily cancel non-collocated interferers (e.g., another interferer on another vehicle operating in proximity to the receiver). For example using the signal sampling method of generating the cancellation signal, it is impossible to predict the phasing (time delay of the non-collocated) interferer, as its position will not necessarily be fixed with respect to the receiver. It is further not possible to completely predict the waveform which needs to be generated using the generated signal approach.
Another approach would be to include the interfering signal in the signal being analyzed and subsequently use signal processing to estimate and thereby cancel the effects of all interferers. However due to collocation of the interferer and the receiver, the potential dynamic range between the interfering signal and the signal of interest is enormous rendering this approach impractical using existing cost-effective technology.
What is needed, and what is disclosed in the present patent application, is techniques which make the use of the techniques for acquiring the cellular environment which are described in Ser. Nos. 12/065,225 and 12/280,716 possible in a cellular environment in which the receiver is restricted to listening during the holes in the interfering signals.